Conversion of the soluble protein, fibrinogen, to the insoluble, polymeric form, fibrin, is a key reaction in normal hemostasis. The exact size and shape of the fibrinogen molecule are controversial, thus the mode of assembly of the molecule to form fibrin is also undertaken. The goal of this research is to answer these questions from a new perspective. We have shown that brief treatment of bovine fibrinogen with an extracellular protease from Pseudomonas alters the properties of the molecule to permit crystallization. We will characterize the enzyme and determine the nature of the physical and chemical changes in fibrinogen resulting from protease action. N and C terminal methods, peptide analysis and separation of the A, BB and chains of the modified molecule will be undertaken, in addition to characterization of the modified molecule by column chromatography, ORD/CD, ultracentrifugation, EM and X-ray diffraction.